An Online Payment Gateway is a technology that facilitates the transfer of payment information between a customer and a merchant. It securely processes credit card and other payment transactions over the internet, ensuring that sensitive data is encrypted and protected. This allows businesses to accept payments from customers without needing to handle physical cash or checks. When a customer makes a purchase on a website, the payment gateway verifies the transaction details with the customer's bank or payment provider. Once approved, the funds are transferred to the merchant's account, completing the sale. Popular examples of payment gateways include PayPal, Stripe, and Square.